This invention relates to liquid, ultra-high molecular weight polyurethane plasticizers, a process for preparing these plasticizers, and to a process for the production of a polyurethane comprising reacting a polyisocyanate component with an isocyanate-reactive component in the presence of these liquid, ultra-high molecular weight polyurethane plasticizers, and to the polyurethanes produced by this process.
Plasticizers are generally used in plastics (i.e., PVC) to adjust the hardness, flexibility and processing characteristics. Plasticizers are also used in some commercial polyurethane elastomer formulations to provide products exhibiting higher flexibility, lower hardness, and lower rebound resulting in increased energy absorption. However, these products potentially embrittle over time due to migration of the plasticizer. Plasticizers that have a minimal effect on hardness and physical properties, and which are non-migrating are desirable for polyurethane elastomers prepared by a one-shot cast elastomer process.
Diurethanes are known and described as suitable stabilizing additives for sealing compounds in, for example, U.S. Pat. No. 4,824,888 and as plasticizers for polyurethane based sealing and adhesive compositions in U.S. Pat. No. 5,525,654.
U.S. Pat. No. 4,824,888 discloses diurethanes which correspond to one of two general formulas, which are useful as stabilizing additives in sealing compounds based on isocyanate-terminated prepolymers of difunctional and trifunctional polyether or polyester polyols and/or polyvinylchloride swellable copolymers of vinyl chloride with monomers from the group vinyl acetate, vinyl propionate and alkyl acrylates. These diurethanes are prepared by the reaction of diols with monoisocvanates and diurethanes prepared from symmetrical diisocyanates with polyether monoalcohols. In particular, the monoalcohols are monofunctional polypropylene glycol monoalkyl ethers having a molecular weight of about 500 to 2000. These diurethanes are also suitable stabilizing agents for isocyanate-terminated polyurethane prepolymers, and for polyvinyl chloride homopolymer or copolymer plastisols.
Moisture curing sealing and/or adhesive compositions based on alkoxysilane-terminated polyurethanes which contain diurethanes as plasticizers are described by U.S. Pat. No. 5,525,654. These diurethanes are prepared from either diol mixtures and monofunctional isocyanates wherein substantially all the free hydroxyl groups are reacted, or from diisocyanates and monofunctional alcohols wherein substantially all the free isocyanate groups are reacted.
Other urethane plasticizers are disclosed in, for example, U.S. Pat. Nos. 4,123,413 and 4,482,408. The urethane plasticizers of U.S. Pat. No. 4,123,413 correspond to one of three general formulas, and are prepared by reaction of an alcohol or a phenol with an isocyanate, from amines and chloroformates, or from chloroformamides and alcohols or phenols in the presence of acid binding agents.
The urethane plasticizer of U.S. Pat. No. 4,482,408 is octyldecyl-butyl urethane and is prepared by reacting an equimolar mixture of octyldecyl isocyanate and n-butyl alcohol. This urethane plasticizer is a mono-urethane described as a straight-chained, saturated, carbamic acid ester and is suitable as a plasticizer for propellant compositions with problems of plasticizer migration which typically occur during propellant storage.
Useful polyurethane plasticizers according to the present invention are based on monoisocyanates or diisocyanates, and at least one compound selected from the group consisting of monoalcohols, polyether polyols, and mixtures thereof, having a molecular weight of more than about 4,000. They are prepared by either adding the alcohol(s) and/or polyether polyol(s) to the monoisocyanates or diisocyanates, or by addition of the monoisocyanates or diisocyanates to the monofunctional alcohol(s) and/or polyether polyol(s). The polyurethane plasticizers are liquid at 25.degree. C. The resulting polyurethane plasticizers do not contain any free hydroxyl- or isocyanate-groups, and thus they are non-reactive and can be added to either isocyanates or polyols to form stable mixtures.
The use of these polyurethane plasticizers in one-shot elastomers has several important benefits:
1) Addition to either the polyol or the isocyanate composition allows one to adjust the mix ratio very favorably, i.e., to adjust a 1:1.5 ratio to an easier to process ratio of 1:1.
2) Addition to either the polyol or isocyanate composition allows one to adjust the viscosities of the two components very favorably, i.e., to obtain viscosities which are similar which facilitates the mixing process.
3) Unmodified polyisocyanates that contain no urethane, allophanate, urea, or biuret groups are usually very incompatible with polyol compositions due to major differences in surface energy (i.e., polarity). Addition of the polyurethane containing plasticizers according to the invention to either the polyisocyanate or both the polyisocyanate and polyol side of one-shot elastomer formulations helps to overcome these incompatibility problems and thus facilitates mixing.
Although it is possible in one-shot elastomer formulations to meter the single components separately and mix them, i.e., in a reactor or mixhead, it is preferred to combine the polyurethane plasticizer with the polyisocyanate and/or the polyol/chain extender blend prior to mixing the isocyanate containing the isocyanate reactive polyol components.
Besides the processing advantages polyurethane plasticizers provide in one-shot polyurethane elastomer formulations, they do not exhibit any substantial migration or lower the physical properties of the final polyurethane elastomer upon aging to the extent observed in state of the art non-urethane group containing plasticizers. As a result, the high performance properties of one-shot polyurethane elastomers are effected minorly upon aging when polyurethane containing plasticizers are used in the formulation.